This invention relates to a boost-retarding device for use on electromagnetic plunger pumps and more particularly for pressure-feed pumps of a fuel oil to pressure-feed injection type burner (a so-called "gun type" burner).
The inventive boost-retarding device slowly retards the discharge pressure rise and reduces the ignition detonation noise of the fuel at the start of operation of the burner.
The inventors of this invention previously disclosed a method of reducing the ignition detonation noise at the start of operation of a pump in Japanese application No. 20,322/1977. This prior art method contemplates an ignition when there is a small discharge flow. To reduce the ignition detonation noise at the start of pump operation, the fuel oil is thottled by means of a cut-off valve disposed on the discharge passage, the fuel oil is gasified, and a part of the oil is compressed with the resulting gas, to cause a time-lag in the pressure transmission characteristics of the fuel oil.
However, it is not easy to set the boost-retarding time of the discharge pressure to an optional value in the above-described method. In addition, that method is not free from the drawback that the cut-off valve performs its cut-off action when the pump stops operating. Then, it leaves a residual pressure on the discharge side and consequently, requires means such as a discharge valve for removing the residual pressure.
An object of the present invention is to improve boost-retarding devices by easily and accurately setting the boost-retarding time at the start of operation of the pump to a desired value.
Another object of the present invention is to easily and accurately set a discharge pressure on a boost-retarding device for an optimum ignition timing and to a desired value.
Yet another object of the present invention is to provide a boost-retading device which does not leave any residual pressure on the discharge side of a pump after it stops operating. Still another object is to eliminate an "after-drip" of the fuel oil from an injection nozzle. A further object is to relieve residual pressure, if any, via a cut-off valve mechanism in a passageway extending from the suction side of the pump. A still further object is to accurately return a plunger to its normal position, when the pump stops.
It is still another object of the present invention to provide a boost-retarding device which ensures stable sucking and discharging actions of the pump at the start of operation and prevents overflow of the fuel oil from the discharge side to a fire chamber, even when the pump stops operating.
Another object of the present invention is to smooth the discharge pulsations of the pump, and to afford a buffer and accumlator action which enhances the efficiency of the pump.
It is yet another object of the present invention to provide a boost-retarding device which can optionally set and adjust a constant discharge pressure of the pump to a desired value.